Plasma reactor with electrode filaments

ABSTRACT

A plasma reactor includes a chamber body having an interior space that provides a plasma chamber and having a ceiling, a gas distributor to deliver a processing gas to the plasma chamber, a pump coupled to the plasma chamber to evacuate the chamber, a workpiece support to hold a workpiece facing the ceiling, an intra-chamber electrode assembly that includes an insulating frame and a filament extending laterally through the plasma chamber between the ceiling and the workpiece support, the filament including a conductor at least partially surrounded by an insulating shell that extends from the insulating frame, and a first RF power source to supply a first RF power to the conductor of the intra-chamber electrode assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 62/489,344, filed Apr. 24, 2017, the entirety ofwhich is incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a plasma reactor, e.g. for depositinga film on, etching, or treating a workpiece such as a semiconductorwafer.

BACKGROUND

Plasma is typically generated using a capacitively-coupled plasma (CCP)source or an inductively-coupled plasma (ICP) source. A basic CCP sourcecontains two metal electrodes separated by a small distance in a gaseousenvironment similar to a parallel plate capacitor. One of the two metalelectrodes are driven by a radio frequency (RF) power supply at a fixedfrequency while the other electrode is connected to an RF ground,generating an RF electric field between the two electrodes. Thegenerated electric field ionizes the gas atoms, releasing electrons. Theelectrons in the gas are accelerated by the RF electric field andionizes the gas directly or indirectly by collisions, producing plasma.

A basic ICP source typically contains a conductor in a spiral or a coilshape. When an RF electric current is flowed through the conductor, RFmagnetic field is formed around the conductor. The RF magnetic fieldaccompanies an RF electric field, which ionizes the gas atoms andproduces plasma.

Plasmas of various process gasses are widely used in fabrication ofintegrated circuits. Plasmas can be used, for example, in thin filmdeposition, etching, and surface treatment.

Atomic layer deposition (ALD) is a thin film deposition technique basedon the sequential use of a gas phase chemical process. Some ALDprocesses use plasmas to provide necessary activation energy forchemical reactions. Plasma-enhanced ALD processes can be performed at alower temperature than non-plasma-enhanced (e.g., ‘thermal’) ALDprocesses.

SUMMARY

In one aspect, a plasma reactor includes a chamber body having aninterior space that provides a plasma chamber and having a ceiling, agas distributor to deliver a processing gas to the plasma chamber, apump coupled to the plasma chamber to evacuate the chamber, a workpiecesupport to hold a workpiece facing the ceiling, an intra-chamberelectrode assembly that includes an insulating frame and a filamentextending laterally through the plasma chamber between the ceiling andthe workpiece support, the filament including a conductor at leastpartially surrounded by an insulating shell that extends from theinsulating frame, and a first RF power source to supply a first RF powerto the conductor of the intra-chamber electrode assembly.

Implementations may include one or more of the following features.

The insulating shell may be a cylindrical shell that surrounds andextends along an entirety of the conductor within the plasma chamber.The insulating shell may be formed from silicon, or an oxide, nitride orcarbide material, or a combination thereof. The insulating shell may beformed from silica, sapphire or silicon carbide. The insulating shellmay be a coating on the conductor. The cylindrical shell may form achannel and the conductor may be suspended in and extends through thechannel, or the conductor may have a hollow channel. A fluid supply maybe configured to circulate a fluid through the channel. The fluid may bea non-oxidizing gas. A heat exchanger may be configured to remove heatfrom or supply heat to the fluid.

The intra-chamber electrode assembly may have a plurality of coplanarfilaments extending laterally through the plasma chamber between theceiling and the workpiece support. The plurality of coplanar filamentsmay be uniformly spaced apart. A surface-to-surface spacing between thecoplanar filaments and the workpiece support surface may be in the rangeof 2 mm to 25 mm. The plurality of coplanar filaments may include linearfilaments. The plurality of coplanar filaments may extend in parallelthrough the plasma chamber. The plurality of coplanar filaments may beuniformly spaced apart.

The shell may be fused to the insulating frame. The shell and theinsulating frame may be a same material composition. The insulatingframe may be formed from silica, or a ceramic material.

In another aspect, a plasma reactor includes a chamber body having aninterior space that provides a plasma chamber and having a ceiling andan insulating support to hold a top electrode, a gas distributor todeliver a processing gas to the plasma chamber, a pump coupled to theplasma chamber to evacuate the chamber, a workpiece support to hold aworkpiece facing the top electrode, an intra-chamber electrode assemblycomprising a filament extending laterally through the plasma chamberbetween the top electrode and the workpiece support, the filamentincluding a conductor at least partially surrounded by an insulatingshell that extends from the insulating frame, and a first RF powersource to supply a first RF power to the conductor of the intra-chamberelectrode assembly.

Implementations may include one or more of the following features.

The top electrode may be formed from silicon, carbon, or a combinationthereof. The insulating frame may be an oxide, nitride, or a combinationthereof. The insulating frame may be formed from silicon oxide, aluminumoxide, or silicon nitride.

In another aspect, a plasma reactor includes a chamber body having aninterior space that provides a plasma chamber and has a ceiling, a gasdistributor to deliver a processing gas to the plasma chamber, a pumpcoupled to the plasma chamber to evacuate the chamber, a workpiecesupport to hold a workpiece, an intra-chamber electrode assembly thatincludes an insulating frame and a filament, the filament including afirst portion extending downwardly from the ceiling and a second portionextending laterally through the plasma chamber between the ceiling andthe workpiece support, the filament including a conductor at leastpartially surrounded by an insulating shell, and, a first RF powersource to supply a first RF power to the conductor of the intra-chamberelectrode assembly.

Implementations may include one or more of the following features.

The intra-chamber electrode assembly may include a plurality offilaments. Each filament may include a first portion extendingdownwardly from the ceiling and a second portion extending laterallythrough the plasma chamber extending laterally through the plasmachamber between the ceiling and the workpiece support. The secondportions of the plurality of filaments may be coplanar. The secondportions of the plurality of filaments may be uniformly spaced apart.The second portions of the plurality of filaments may be linear.

The support may include a downwardly projecting side wall that surroundsa volume between the ceiling and the second portion of the filament. Theside wall may be formed from silicon oxide or a ceramic material. Theceiling may include an insulating frame, and the filaments may extendout of the insulating frame. The shell may be fused to the frame. Theshell and the support may have a same material composition. Theinsulating frame may be formed from silica, or a ceramic material.

In another aspect, a plasma reactor includes a chamber body having aninterior space that provides a plasma chamber and having a ceiling, agas distributor to deliver a processing gas to the plasma chamber, apump coupled to the plasma chamber to evacuate the chamber, a workpiecesupport to hold a workpiece, and an intra-chamber electrode assembly.The intra-chamber electrode assembly includes an insulating frame, afirst plurality of coplanar filaments that extend laterally through theplasma chamber between the ceiling and the workpiece support along afirst direction, and a second plurality of coplanar filaments thatextend in parallel through the plasma chamber along a second directionperpendicular to the first direction. Each filament of the first andsecond plurality of filaments includes a conductor at least partiallysurrounded by an insulating shell. A first RF power source supplies afirst RF power to the conductor of the intra-chamber electrode assembly.

Certain implementations may have one or more of the followingadvantages. Plasma uniformity may be improved. Plasma processrepeatability may be improved. Metal contamination may be reduced.Particle generation may be reduced. Plasma charging damage may bereduced. Uniformity of plasma may be maintained over different processoperating conditions. Plasma power coupling efficiency may be improved.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side view diagram of an example of a plasmareactor.

FIG. 2 is a schematic side view diagram of another example of a plasmareactor.

FIG. 3 is a perspective view of an example of an intra-chamber electrodeassembly according to FIG. 2.

FIGS. 4A-4C are schematic cross-sectional perspective view diagrams ofvarious examples of a filament of an intra-chamber electrode assembly.

FIG. 5A is a schematic top view diagram of a portion of an intra-chamberelectrode assembly.

FIGS. 5B-C are cross-sectional schematic side view diagrams of anintra-chamber electrode assembly with different plasma region states.

FIGS. 6A-C are schematic top view diagrams of various examples ofintra-chamber electrode assembly configurations.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Plasma uniformity in a conventional CCP source is typically determinedby electrode(s) size and inter-electrode distance, as well as by gaspressure, gas composition, and applied RF power. At higher radiofrequencies, additional effects may become significant or even dominatenon-uniformities due to the presence of standing waves or skin effects.Such additional effects becomes more pronounced at higher frequenciesand plasma densities.

Plasma uniformity in a conventional ICP source is typically determinedby the configuration of ICP coil(s) including its size, geometry,distance to workpiece, and associated RF window location, as well as bygas pressure, gas composition, and power. In case of multiple coils orcoil segments, the current or power distribution and their relativephase, if driven at same frequency, might also be a significant factor.Power deposition tends to occur within several centimeters under oradjacent to ICP coils due to skin effect, and such localized powerdeposition typically leads to process non-uniformities that reflect thecoil geometries. Such plasma non-uniformity causes a potentialdifference across a workpiece, which can also lead to plasma chargingdamage (e.g., transistor gate dielectric rupture).

A large diffusion distance is typically needed for improved uniformityof ICP source. However, a conventional ICP source with a thick RF windowis typically inefficient at high gas pressures due to low powercoupling, which leads to high drive current resulting in high resistivepower losses. In contrast, an intra-chamber electrode assembly does notneed to have an RF window, but only a cylindrical shell. This canprovide better power coupling and better efficiency.

In a plasma chamber with a moving workpiece support, the movingworkpiece support may be DC grounded through, for example, a rotarymercury coupler, brushes, or slip rings. However, the moving workpiecesupport may not be adequately grounded at radio frequencies. The RFground path should have substantially lower impedance than the plasmafor it to be an adequate RF ground. The lack of an adequate RF groundpath may make it difficult to control ion energy at the workpiece andreduce the repeatability of the process.

A plasma source with the following properties is thus desired: it canefficiently produce a uniform plasma with the desired properties (plasmadensity, electron temperature, ion energy, dissociation, etc.) over theworkpiece size; it is tunable for uniformity over the operating window(e.g. pressure, power, gas composition); it has stable and repeatableelectrical performance even with a moving workpiece; and it does notgenerate excessive metal contaminants or particles. An intra-chamberelectrode assembly might be better able to provide one or more of theseproperties.

FIG. 1 is a schematic side view diagram of an example of a plasmareactor. A plasma reactor 100 has a chamber body 102 enclosing aninterior space 104 for use as a plasma chamber. The interior space 104can be cylindrical, e.g., for processing of circular semiconductorwafers. The chamber body 102 has a support 106 located near the ceilingof the plasma reactor 100, which supports a top electrode 108. The topelectrode can be suspended within the interior space 104 and spaced fromthe ceiling, abut the ceiling, or form a portion of the ceiling. Someportions of the side walls of the chamber body 102 can be groundedindependent of the top electrode 108.

A gas distributor 110 is located near the ceiling of the plasma reactor100. In some implementations, the gas distributor 110 is integrated withthe top electrode 108 as a single component. The gas distributor 110 isconnected to a gas supply 112. The gas supply 112 delivers one or moreprocess gases to the gas distributor 110, the composition of which candepend on the process to be performed, e.g., deposition or etching. Avacuum pump 113 is coupled to the interior space 104 to evacuate theplasma reactor. For some processes, the chamber is operated in the Torrrange, and the gas distributor 110 supplies argon, nitrogen, oxygenand/or other gases.

A workpiece support pedestal 114 for supporting a workpiece 115 ispositioned in the plasma reactor 100. The workpiece support pedestal 114has a workpiece support surface 114 a facing the top electrode 108.

In some implementations, the workpiece support pedestal 114 includes aworkpiece support electrode 116 inside the workpiece support pedestal114. In some implementations, the workpiece support electrode 116 may begrounded or connected to an impedance or circuit which is grounded. Insome implementations, an RF bias power generator 142 is coupled throughan impedance match 144 to the workpiece support electrode 116. Theworkpiece support electrode 116 may additionally include anelectrostatic chuck, and a workpiece bias voltage supply 118 may beconnected to the workpiece support electrode 116. The RF bias powergenerator 142 may be used to generate plasma, control electrode voltageor electrode sheath voltage, or to control ion energy of the plasma.

Additionally, the pedestal 114 can have internal passages 119 forheating or cooling the workpiece 115. In some implementations, anembedded resistive heater can be provided inside the pedestal, e.g.,inside the internal passages 119.

In some implementations, the workpiece support pedestal 114 is heatedthrough radiant and/or convective heating from a heating element locatedwithin a bottom interior space 133, and/or by a resistive heater on orembedded in the pedestal 114.

An intra-chamber electrode assembly 120 is positioned in the interiorspace 104 between the top electrode 108 and the workpiece supportpedestal 114. This electrode assembly 120 includes one or more filaments310 that extend laterally in the chamber over the support surface 114 aof the pedestal 114. At least a portion of the filaments of theelectrode assembly 120 over the pedestal 114 extends parallel to thesupport surface 114 a. A top gap 130 is formed between the top electrode108 and the intra-chamber electrode assembly 120. A bottom gap 132 isformed between the workpiece support pedestal 114 and the intra-chamberelectrode assembly 120.

The electrode assembly 120 is driven by an RF power source 122. The RFpower source 122 can apply power to the one or more filaments of theelectrode assembly 120 at frequencies of 1 MHz to over 300 MHz. For someprocesses, the RF power source 120 provides a total RF power 100 W tomore than 2 kW at a frequency of 60 MHz.

In some implementations, it may be desirable to select the bottom gap132 to cause plasma generated radicals, ions or electrons to interactwith the workpiece surface. The selection of gap isapplication-dependent and operating regime dependent. For someapplications wherein it is desired to deliver a radical flux (but verylow ion/electron flux) to the workpiece surface, operation at larger gapand/or higher pressure may be selected. For other applications whereinit is desired to deliver a radical flux and substantial plasmaion/electron flux) to the workpiece surface, operation at smaller gapand/or lower pressure may be selected. For example, in somelow-temperature plasma-enhanced ALD processes, free radicals of processgases are necessary for the deposition or treatment of an ALD film. Afree radical is an atom or a molecule, has an unpaired valence electron.A free radical is typically highly chemically reactive towards othersubstances. The reaction of free radicals with other chemical speciesoften plays an important role in film deposition. However, free radicalsare typically short-lived due to their high chemical reactivity, andtherefore cannot be transported very far within their lifetime. Placingthe source of free radicals, namely the intra-chamber electrode assembly120 acting as a plasma source, close to the surface of the workpiece 115can increase the supply of free radicals to the surface, improving thedeposition process.

The lifetime of a free radical typically depends on the pressure of thesurrounding environment. Therefore, a height of the bottom gap 132 thatprovides satisfactory free radical concentration can change depending onthe expected chamber pressure during operation. In some implementations,if the chamber is to be operated at a pressure in the range of 1-10Torr, the bottom gap 132 is less than 1 cm.

In other low(er) temperature plasma-enhanced ALD processes, exposure toplasma ion flux (and accompanying electron flux) as well as radical fluxmay be necessary for deposition and treatment of an ALD film. In someimplementations, if the chamber is to be operated at a pressure in therange of 1-10 Torr, the bottom gap 132 is less than 5 cm—for example2-25 mm, e.g., 5 mm. Lower operating pressures may operate at largergaps due to lower volume recombination rate with respect to distance. Inother applications, such as etching, lower operating pressure istypically used (less than 100 mTorr) and the gap may be increased.

In such applications where the bottom gap 132 is small, the plasmagenerated by the electrode assembly 120 can have significantnon-uniformities between the filaments, which may be detrimental toprocessing uniformity of the workpiece. By moving the workpiece throughthe plasma having spatial non-uniformities, the effect of the plasmaspatial non-uniformities on the process can be mitigated by atime-averaging effect, i.e., the cumulative plasma dose received by anygiven region of the workpiece after a single pass through the plasma issubstantially similar.

The top gap may be selected large enough for plasma to develop betweenintra-chamber electrode assembly and top electrode (or top of chamber).In some implementations, if the chamber is to be operated at a pressurein the range of 1-10 Torr, the top gap 130 may be between 0.5-2 cm,e.g., 1.25 cm.

The top electrode 108 can be configured in various ways. In someimplementations, the top electrode is connected to an RF ground 140. Insome implementations, the top electrode is electrically isolated(‘floating’). In some implementations, the top electrode 108 is biasedto a bias voltage. The bias voltage can be used to controlcharacteristics of the generated plasma, including the ion energy. Insome implementations, the top electrode 108 is driven with an RF signal.For example, driving the top electrode 108 with respect to the workpiecesupport electrode 116 that has been grounded can increase the plasmapotential at the workpiece 115. The increased plasma potential can causean increase in ion energy to a desired value.

The top electrode 108 can be formed of different process-compatiblematerials. Various criteria for process-computability include amaterial's resistance to etching by the process gasses and resistance tosputtering from ion bombardment. Furthermore, in cases where a materialdoes get etched, a process-compatible material preferably forms avolatile, or gaseous, compound which can be evacuated by the vacuum pump113, and not form particles that can contaminate the workpiece 115.Accordingly, in some implementations, the top electrode is made ofsilicon. In some implementations, the top electrode is made of siliconcarbide. In some implementations, the top electrode is made ofcarbon-based material.

In some implementations, the top electrode 108 may be omitted. In suchimplementations, RF ground paths may be provided by the workpiecesupport electrode or by a subset of coplanar filaments of the electrodeassembly 120 or by a chamber wall or other ground-referenced surface incommunication with plasma.

In some implementations, a fluid supply 146 circulates a fluid throughthe intra-chamber electrode assembly 120. In some implementations, aheat exchanger 148 is coupled to the fluid supply 146 to remove orsupply heat to the fluid.

Depending on chamber configuration and supplied processing gasses, theplasma reactor 100 could provide an ALD apparatus, an etching apparatus,a plasma treatment apparatus, a plasma-enhanced chemical vapordeposition apparatus, a plasma doping apparatus, or a plasma surfacecleaning apparatus.

FIG. 2 is a schematic diagram of another example of a plasma reactor200. In this example, which is the same as FIG. 1 except as described,the intra-chamber electrode assembly 120 is curved to be supported bythe support 106, and the fluid supply 146 can be coupled to theintra-chamber electrode assembly 120 through the support 106. Incontrast, in the example of FIG. 1, the filaments of the electrodeassembly can emerge from and be supported by the side walls of thechamber body 102.

FIG. 3 is a perspective view of an example of an intra-chamber electrodeassembly according to FIG. 2. It shows the support 106, top electrode108, the top gap 130, and the intra-chamber electrode assembly 120. Theintra-chamber electrode assembly 120 includes one or more filaments 310that extend laterally through the plasma chamber. The filaments includea central portion 312 that extends over the pedestal 114 (See FIG. 2)and end portions 314 that are curved upward to be supported from thesupport 106. This configuration can provide for a compact installationand accessibility of the filaments from the top of the plasma reactor100.

FIGS. 4A-C are schematic diagrams of various examples of a filament ofan intra-chamber electrode assembly. Referring to FIG. 4A, a filament400 of the intra-chamber electrode assembly 120 is shown. The filament400 includes a conductor 410 and a cylindrical shell 420 that surroundsand extends along the conductor 410. A channel 430 is formed by the gapbetween the conductor 410 and the cylindrical shell 420. The cylindricalshell 420 is formed of a non-metallic material that is compatible withthe process. In some implementations, the cylindrical shell issemiconductive. In some implementations, the cylindrical shell isinsulative.

The conductor 410 can be formed of various materials. In someimplementations, the conductor 410 is a solid wire, e.g., a single solidwire with a diameter of 0.063″. Alternatively, the conductor 410 can beprovided by multiple stranded wires. In some implementations, theconductor contains 3 parallel 0.032″ stranded wires. Multiple strandedwires can reduce RF power losses through skin effect. Litz wire canfurther reduce the skin effect.

A material with high electrical conductivity, e.g., above 10⁷ Siemen/m,is used, which can reduce resistive power losses. In someimplementations, the conductor 410 is made of copper or an alloy ofcopper. In some implementations, the conductor is made of aluminum.

Undesired material sputtering or etching can lead to processcontamination or particle formation. Whether the intra chamber electrodeassembly 120 is used as a CCP or an ICP source, undesired sputtering oretching can occur. The undesired sputtering or etching may be caused byexcessive ion energy at the electrode surface. When operating as a CCPsource, an oscillating electric field around the cylindrical shell isnecessary to drive the plasma discharge. This oscillation leads tosputtering or etching of materials, as all known materials have asputtering energy threshold that is lower than the corresponding minimumoperating voltage of a CCP source. When operated as an ICP source,capacitive coupling of the filament 400 to the plasma creates anoscillating electric field at nearby surfaces, which also causessputtering of materials. The problems resulting from undesired materialsputtering or etching may be mitigated by using a process-compatiblematerial for the outer surface of the filament 400 exposed to theinterior space 104 (e.g., the cylindrical shell 420).

In some implementations, the cylindrical shell 420 is formed of aprocess-compatible material such as silicon, e.g., a high resistivitysilicon, an oxide material, a nitride material, a carbide material, aceramic material, or a combination thereof. Examples of oxide materialsinclude silicon dioxide (e.g., silica, quartz) and aluminum oxide (e.g.,sapphire). Examples of carbide materials include silicon carbide.Examples of nitride materials include silicon nitride. Ceramic materialsor sapphire may be desirable for some chemical environments includingfluorine-containing environments or fluorocarbon containingenvironments. In chemical environments containing ammonia,dichlorosilane, nitrogen, and oxygen, use of silicon, silicon carbide,or quartz may be desirable.

In some implementations, the cylindrical shell 420 has a thickness of0.1 mm to 3 mm, e.g., 1 mm. The shell 420 can have an inner diameter of2-4 mm, e.g., 2 mm.

In some implementations, a fluid is provided in the channel 430. In someimplementations, the fluid is a non-oxidizing gas to purge oxygen tomitigate oxidization of the conductor 410. Examples of non-oxidizinggases are nitrogen and argon. In some implementations, the non-oxidizinggas is continuously flowed through the channel 430, e.g., by the fluidsupply 146, to remove residual oxygen or water vapor.

The heating of conductor 410 can make the conductor more susceptible tooxidization. The fluid can provide cooling to the conductor 410, whichmay heat up from supplied RF power. In some implementations, the fluidis circulated through the channel 430, e.g., by the fluid supply 146, toprovide forced convection temperature control, e.g., cooling or heating.

In some implementations, the fluid may be at or above atmosphericpressure to prevent breakdown of the fluid. This can prevent unwantedplasma formation in tube. The pressure in the channel 430 can be atleast 100 Torr.

Referring to FIG. 4B, in some implementations of the filament 400, theconductor 410 has a coating 420. In some implementations, the coating420 is an oxide of the material forming the conductor (e.g., aluminumoxide on an aluminum conductor). In some implementations, the coating420 is silicon dioxide. In some implementations, the coating 420 isformed in-situ in the plasma reactor 100 by, for example, a reaction ofsilane, hydrogen, and oxygen to form a silicon dioxide coating. In-situcoating may be beneficial as it can be replenished when etched orsputtered. The coating may be 0.1-10 microns thick.

Referring to FIG. 4C, in some implementations of the filament 400, theconductor 410 is hollow, and a hollow channel 440 is formed inside theconductor 410. In some implementations, the hollow channel 440 can carrya fluid as described in FIG. 4A. The conductor can be hollow tube withan outer diameter of about 1-4 mm, e.g., 2 mm, and a wall thickness of0.25-1 mm, e.g., 0.5 mm. A coating of the process-compatible materialcan cover the conductor 410 to provide the cylindrical shell 420. Insome implementations, the coating 420 is an oxide of the materialforming the conductor (e.g., aluminum oxide on an aluminum conductor).In some implementations, the hollow conductor 410 has an outer diameterof 2 mm, with a wall thickness of 0.5 mm.

Returning to FIGS. 1 and 2, the filaments 400 are supported by andextend from a frame. The frame is formed of a process-compatiblematerial such as an oxide material, a nitride material, a carbidematerial, a ceramic material, or a combination thereof. Examples ofoxide materials include silicon dioxide (e.g., silica, quartz) andaluminum oxide (e.g., sapphire). Examples of carbide materials includesilicon carbide. In some implementations, the frame and the shell of thefilament 310 are formed of the same material, e.g., quartz.

The shell of the filament 400 can be fused to the frame. This can createa fluid-tight seal to prevent process gas from reaching the conductor,and thus can improve lifetime of the reactor, and reduce the likelihoodof contamination.

In some implementations, e.g., as shown in FIG. 1, the filaments 400extend horizontally from the frame. In some implementations, e.g., asshown in FIG. 2, the frame provides a portion of the ceiling and thefilaments 400 extend downwardly from the frame.

In some implementations, e.g., as shown in FIGS. 2 and 3, the frame canbe provided by the support 106. In other implementations, the frame is aseparate body, e.g., a body mounted to the ceiling or side walls 102. Insome implementations, the frame is provided by the side walls of thechamber. The chamber walls can be conductive, but the insulating shellcan isolate the conductor from the chamber wall.

As shown in FIG. 1, if the filaments 400 project horizontally from theframe, then the frame can be a body 105 that extends downwardly tosurround the top gap 130. Alternatively, e.g., as shown in FIG. 3, ifthe filaments extend downwardly from the ceiling, the support 106 caninclude a downwardly projecting wall 107 that surrounds the top gap 130.The body 105 or wall 107 can be integrally formed or fused to thesupport 106 to provide a fluid-tight seal.

FIG. 5A is a schematic diagram of a portion of an intra-chamberelectrode assembly. An intra-chamber electrode assembly 500 includesmultiple filaments 400 attached at a support 502. The electrode assembly500 can provide the electrode assembly 120, and the filaments 400 canprovide the filaments, e.g., filaments 310, of the electrode assembly120. In some implementations, the filaments extend in parallel to eachother.

The filaments 400 are separated from one another by a filament spacing510. The filament spacing 510 can be the surface-to-surface distance;for parallel filaments the spacing can be measured perpendicular to thelongitudinal axis of the filaments. The spacing 510 can impact plasmauniformity. If the spacing is too large, then the filaments can createshadowing and non-uniformity. On the other hand, if the spacing is toosmall, the plasma cannot migrate between the top gap 130 and the bottomgap 132, and non-uniformity will be increased or ion density or freeradical density will be reduced. In some implementations, the filamentspacing 510 is uniform across the assembly 500.

The filament spacing 510 can be 3 to 20 mm, e.g., 8 mm. At highpressure, e.g., 2-10 torr in N₂, the filament spacing may be 20 mm to 3mm. A compromise over the pressure range may be 5-10 mm. At lowerpressure and greater distance to workpiece larger spacing may beeffectively used.

FIGS. 5B-C are cross-sectional schematic diagrams of an intra-chamberelectrode assembly with different plasma region states. Referring toFIG. 5B, a plasma region 512 surrounds the filaments 400. The plasmaregion 512 has an upper plasma region 514 and a lower plasma region 516.The upper plasma region 514 is located at the top gap 130 and the lowerplasma region 516 is located at the bottom gap 132. As shown in FIG. 5B,the upper plasma region 514 and the lower plasma region 516 is connectedthrough the gaps between the filaments 400, forming a continuous plasmaregion 512. This continuity of the plasma regions 512 is desirable, asthe regions 514 and 516 ‘communicate’ with each other through exchangeof plasma. Particularly for a monopolar drive (all the filamentsconnected to same power source) and a grounded top electrode as the mainground path, the exchanging of plasma helps keep the two regionselectrically balanced, aiding plasma stability and repeatability.

In the case of a monopolar drive with the filaments driven with respectto some other ground and in the absence of a top ground (such as with agrounded workpiece) then plasma need not be generated above thefilaments. Also in the case of differential drive (e.g. alternatingfilaments connect to each side of power supply output), then plasma canbe generated between the filaments, so plasma above the filaments is notnecessary. However, in these cases a grounded top electrode should notbe detrimental.

Referring to FIG. 5C, in this state, the upper plasma region 514 and thelower plasma region 516 is not connected to each other. This ‘pinching’of the plasma region 512 is not desirable for plasma stability. Theshape of the plasma region 512 can be modified by various factors toremove the plasma region discontinuity or improve plasma uniformity.

In general, the regions 512, 514, and 516 can have a wide range ofplasma densities, and are not necessarily uniform. Furthermore, thediscontinuities between the upper plasma region 514 and the lower plasmaregion 516 shown in FIG. 5C represents a substantially low plasmadensity relative to the two regions, and not necessarily a complete lackof plasma in the gaps.

The top gap 130 is a factor affecting the shape of the plasma region.Depending on the pressure, when the top electrode 108 is grounded,reducing the top gap 130 typically leads to a reduction of plasmadensity in the upper plasma region 514. Specific values for the top gap130 can be determined based on computer modelling of the plasma chamber.For example, the top gap 130 can be 3 mm to 8 mm, e.g., 4.5 mm.

The bottom gap 132 is a factor affecting the shape of the plasma region.Depending on the pressure, when the workpiece support electrode 116 isgrounded, reducing the bottom gap 132 typically leads to a reduction ofplasma density in the lower plasma region 516. Specific values for thebottom gap 132 can be determined based on computer modelling of theplasma chamber. For example, the bottom gap 132 can be 3 mm to 9 mm,e.g., 4.5 mm.

The phase of the RF signal driving adjacent filaments 400 is a factoraffecting the shape of the plasma region. When the phase difference ofthe two RF signals driving the adjacent filaments is set to 0 degrees(‘monopolar’, or ‘singled-ended’), the plasma region is pushed out fromthe gaps between the filaments 400, leading to discontinuity ornon-uniformity. When the phase difference of the RF signals driving theadjacent filaments is set to 180 degrees (‘differential’), the plasmaregion is more strongly confined between the filaments 400. Any phasedifference between 0 and 360 degrees can be used to affect the shape ofthe plasma region 512.

The grounding of the workpiece support electrode 116 is a factoraffecting the shape of the plasma region. Imperfect RF grounding of theelectrode 116 in combination with 0 degrees of phase difference betweenthe RF signals driving the adjacent filaments pushes the plasma regiontowards the top gap. However, if adjacent filaments, e.g., filaments 402and 404 are driven with RF signals that have 180 degrees of phasedifference, the resulting plasma distribution is much less sensitive toimperfect RF grounding of the electrode 116. Without being limited toany particular theory, this can be because the RF current is returnedthrough the adjacent electrodes due to the differential nature of thedriving signals.

In some implementations, the intra-chamber electrode assembly 500 caninclude a first group and a second group of filaments 400. The firstgroup and the second group can be spatially arranged such that thefilaments alternate between the first group and the second group. Forexample, the first group can include the filament 402, the second groupcan include the filaments 400 and 404. The first group can be driven bya first terminal 522 a of an RF power supply 522 and the second groupcan be driven by a second terminal 522 b of the RF power supply 522. TheRF power supply 522 can be configured to provide a first RF signal atthe terminal 522 a and a second RF signal at terminal 522 b. The firstand second RF signals can have a same frequency and a stable phaserelationship to each other. For example, the phase relationship caninclude 0 degrees and 180 degrees. In some implementations, the phaserelationship between the first and the second RF signals provided by theRF power supply 522 can be tunable between 0 and 360. In someimplementations, the RF supply 522 can include two individual RF powersupplies that are phase-locked to each other.

FIGS. 6A-C are schematic diagrams of various examples of intra-chamberelectrode assembly configurations. Referring to FIG. 6A, anintra-chamber electrode assembly 600 includes a first interdigitatedelectrode subassembly 620 and a second interdigitated electrodesubassembly 630. The subassembly 620 and 630 each has multiple parallelfilaments 400 that are connected by a bus 650 at one end. In someimplementations, the bus 650 connecting the filaments 400 is locatedoutside of the interior space 104. In some implementations, the bus 650connecting the filaments 400 is located in the interior space 104. Thefirst interdigitated electrode subassembly 620 and a secondinterdigitated electrode subassembly 630 are oriented parallel to eachother such that the filaments of the subassemblies 620 and 630 areparallel to each other.

Referring to FIG. 6B, an intra-chamber electrode assembly 602 includes afirst electrode subassembly 622 and a second electrode subassembly 632configured such that the filaments of the subassemblies 622 and 632extend at a non-zero angle, e.g., perpendicular, to each other.

The intra-chamber electrode assembly 602 can be driven with RF signalsin various ways. In some implementations, the subassembly 622 andsubassembly 632 are driven with a same RF signal with respect to an RFground. In some implementations, the subassembly 622 and subassembly 632are driven with a differential RF signal. In some implementations, thesubassembly 622 is driven with an RF signal, and subassembly 632 isconnected to an RF ground.

Referring to FIG. 6C, an intra-chamber electrode assembly 604 includes afirst electrode subassembly 624 and a second electrode subassembly 634that are overlaid. The first electrode subassembly 624 and the secondelectrode subassembly 634 each has multiple parallel filaments 400 thatare connected by buses 660 and 662 in both ends. The first electrodesubassembly 624 and the second electrode subassembly 634 are configuredsuch that the filaments of the subassemblies 624 and 634 are parallel toeach other, with the filaments of the subassemblies 624, 635 arranged inalternating pattern.

The intra-chamber electrode assembly 604 can be driven with RF signalsin various ways. In some implementations, the subassembly 624 andsubassembly 634 are driven with a same RF signal with respect to an RFground. In some implementations, the subassembly 624 and subassembly 634are driven with a differential RF signal. In some implementations, thesubassembly 624 is driven with an RF signal, and the subassembly 634 isconnected to an RF ground.

In some implementations, the intra-chamber electrode assembly 604 isdriven in a single-ended manner with an RF signal using a center-feed640. The center-feed 640 is connected to an X-shaped current splitter642 at the center. The four corners of the subassemblies 624 and 634 areconnected to the X-shaped current splitter 642 using vertical feedstructures.

In general, differential driving of the subassemblies 620, 622, 624 andthe respective subassemblies 630, 632, 634 can improve plasma uniformityor process repeatability when an adequate RF ground cannot be provided(e.g., RF ground through a rotary mercury coupler, brushes, or sliprings).

Particular embodiments of the invention have been described. However,other embodiments are possible. For example:

-   -   The workpiece could be held stationary within the plasma        chamber.    -   The platform could be moved linearly or rotated such that the        workpiece moves in the plasma chamber.

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A plasma reactor comprising: a chamber bodyhaving an interior space that provides a plasma chamber and having aceiling; a gas distributor to deliver a processing gas to the plasmachamber; a pump coupled to the plasma chamber to evacuate the chamber; aworkpiece support to hold a workpiece facing the ceiling; anintra-chamber electrode assembly comprising an insulating frame and afilament extending laterally through the plasma chamber between theceiling and the workpiece support, the filament including a conductor atleast partially surrounded by an insulating shell that extends from theinsulating frame; and a first RF power source to supply a first RF powerto the conductor of the intra-chamber electrode assembly.
 2. The plasmareactor of claim 1, wherein the insulating shell comprises a cylindricalshell that surrounds and extends along an entirety of the conductorwithin the plasma chamber.
 3. The plasma reactor of claim 1, wherein theinsulating shell is formed from silicon, or an oxide, nitride or carbidematerial, or a combination thereof.
 4. The plasma reactor of claim 3,wherein the insulating shell is formed from silica, sapphire or siliconcarbide.
 5. The plasma reactor of claim 1, wherein the insulating shellcomprises a coating on the conductor.
 6. The plasma reactor of claim 1,wherein the cylindrical shell forms a channel and the conductor issuspended in and extends through the channel.
 7. The plasma reactor ofclaim 6, further comprising a fluid supply configured to circulate afluid through the channel.
 8. The plasma reactor of claim 7, wherein thefluid comprises a non-oxidizing gas.
 9. The plasma reactor of claim 7,comprising a heat exchanger configured to remove heat from or supplyheat to the fluid.
 10. The plasma reactor of claim 1, wherein theconductor comprises a hollow channel.
 11. The plasma reactor of claim10, further comprising a fluid supply configured to circulate a fluidthrough the channel.
 12. The plasma reactor of claim 11, comprising aheat exchanger configured to remove heat from or supply heat to thefluid.
 13. The plasma reactor of claim 1, wherein the intra-chamberelectrode assembly comprises a plurality of coplanar filaments extendinglaterally through the plasma chamber between the ceiling and theworkpiece support.
 14. The plasma reactor of claim 13, wherein theplurality of coplanar filaments are uniformly spaced apart.
 15. Theplasma reactor of claim 14, wherein a surface-to-surface spacing betweenthe coplanar filaments is in the range of 2 mm to 25 mm.
 16. The plasmareactor of claim 13, wherein the plurality of coplanar filamentscomprise linear filaments.
 17. The plasma reactor of claim 16, whereinthe plurality of coplanar filaments extend in parallel through theplasma chamber.
 18. The plasma reactor of claim 17, wherein theplurality of coplanar filaments are uniformly spaced apart.
 19. Theplasma reactor of claim 1, wherein the shell is fused to the insulatingframe.
 20. The plasma chamber of claim 1, wherein the shell and theinsulating frame are a same material composition.
 21. The plasma chamberof claim 1, wherein the insulating frame is formed from silica, or aceramic material.